The present application is related to the following applications which are incorporated herein by reference: U.S. patent application entitled xe2x80x9cLOW POWER GATE TRIGGER CIRCUIT FOR CONTROLLING A SILICON-CONTROLLED RECTIFIER CIRCUIT,xe2x80x9d application Ser. 09/797,264, and U.S. patent application entitled xe2x80x9cAPPARATUS AND METHOD FOR ISOLATING A TRIGGER CIRCUIT OF A SILICON-CONTROLLED RECTIFIER,xe2x80x9d application Ser. No. 09/797,265. All of the above applications are filed simultaneously herewith on Feb. 28, 2001.
This invention relates generally to electronic devices used in connection with power supplies. More particularly, this invention relates to a technique for utilizing a snubber capacitor in a power supply trigger circuit.
High voltage applications of power electronic switches require that many power electronic devices be in series. Each of these devices must have a gate trigger circuit and this circuit must have voltage isolation. This voltage isolation is typically attained by using transformers with isolated windings.
It would be highly desirable to achieve voltage-isolation without incurring the expense of transformers with isolated windings.
An embodiment of the present invention is a power electronic switch circuit that includes a silicon-controlled rectifier and a silicon-controlled rectifier gate trigger circuit coupled to the silicon-controlled rectifier. A snubber capacitor is coupled to the silicon-controlled rectifier and the silicon-controlled rectifier gate trigger circuit. The snubber capacitor generates a snubber capacitor voltage during an OFF state of the silicon-controlled rectifier. The snubber capacitor voltage is then used to power the silicon-controlled rectifier gate trigger circuit. The circuit also includes a resister-zener diode circuit coupled to the snubber capacitor and all auxiliary capacitor. The auxiliary capacitor is charged through the resister-zener diode circuit by the snubber capacitor voltage. A voltage regulator is coupled between the auxiliary capacitor and the silicon-controlled rectifier.
In accordance with the invention, the problem of providing a power supply for the gate trigger circuit and the problem of providing voltage isolation are solved by using the snubber capacitor voltage that is developed during the OFF state of the silicon-controlled rectifier. Sufficient charge is collected from the snubber capacitor to power the gate trigger circuit for a few seconds. For the specific application of soft switching a circuit to the ON state when there is a parallel mechanical circuit breaker or circuit closer, this duration of power supply is adequate.